Thin film solar cells composed of percolating networks of liquid electrolyte and dye-coated sintered titanium dioxide were developed by Dr. Michael Grätzel and coworkers at the Swiss Federal Institute of Technology. These photovoltaic devices fall within a general class of cells referred to as dye-sensitized solar cells (“DSSCs”). Conventionally, fabrication of DSSCs requires a high temperature sintering process (>about 400° C.) to achieve sufficient interconnectivity between the nanoparticles and enhanced adhesion between the nanoparticles and a transparent substrate. Although the photovoltaic cells of Grätzel are fabricated from relatively inexpensive raw materials, the high temperature sintering technique used to make these cells limits the cell substrate to rigid transparent materials, such as glass, and consequently limits the manufacturing to batch processes and the applications to those tolerant of the rigid structure.
Presently, many applications would benefit from the availability of a flexible photovoltaic cell or module. For example, greeting cards that play music or produce other audiovisual outputs are presently powered by batteries. Generally, conventional batteries lack flexibility and thus present the risk of breakage or creation of shorts when mounted on flexible substrates. They also add thickness and weight to the greeting card. Similarly, so-called “smart cards” (i.e., electronic cards used for identification purposes or to perform various functions) presently employ rigid conventional batteries that add bulk and limit substrate options.